The present invention relates to mounting adapters, and in particular to snap on mounting adapters for thermal sensing switches.
Thermal sensing electrical switching devices, or thermal switches, of various configurations are generally well known. For example, thermocouples, resistive thermal devices (RTDs) and thermistors are used for measuring temperature in various applications. Such sensors provide an electrical analog signal, such as a voltage or a resistance, which changes as a function of temperature. Monolithic temperature sensors are also known. For example, a diode connected bipolar transistor can be used for temperature sensing. More specifically, a standard bipolar transistor can be configured with the base and emitter terminals shorted together. With such a configuration, the base collector junction forms a diode. When electrical power is applied, the voltage drop across the base collector junction varies relatively linearly as a function of temperature. Thus, such diode connected bipolar transistors have been known to be incorporated into various integrated circuits for temperature sensing. Such devices are useful in providing relatively accurate temperature measurements; however, they are generally not used in control applications to control electrical equipment.
Precision thermostats are generally used in such control applications. The thermal switch is one form of precision thermostat used in control applications to switch on or off heaters, fans, and other electrical equipment at specific temperatures. Such temperature switches typically consist of a sensing element which provides a displacement as a function of temperature and a pair of electrical contacts. The sensing element is typically mechanically interlocked with the pair of electrical contacts to either make or break the electrical contacts at predetermined temperature set points. The temperature set points are defined by the particular sensing element utilized.
Various types of sensing elements are known which provide a displacement as a function of temperature. For example, mercury bulbs, magnets and bi-metallic elements are known to be used in such temperature switches. Mercury bulb thermal sensors have a mercury filled bulb and an attached glass capillary tube which acts as an expansion chamber. Two electrical conductors are disposed within the capillary at a predetermined distance apart. The electrical conductors act as an open contact. As temperature increases, the mercury expands in the capillary tube until the electrical conductors are shorted by the mercury forming a continuous electrical path. The temperature at which the mercury shorts the electrical conductors is a function of the separation distance of the conductors.
Magnetic reed switches have also been known to be used as temperature sensors in various thermal switches. Such reed switch sensors generally have a pair of toroidal magnets separated by a ferrite collar and a pair of reed contacts. At a critical temperature known as the Curie point, the ferrite collar changes from a state of low reluctance to high reluctance to allow the reed contacts to open.
Bi-metallic thermal switch elements typically consist of two strips of materials having different rates of thermal expansion fused into one bi-metallic disc-shaped element. Precise physical shaping of the disc element and unequal expansion of the two materials cause the element to change shape rapidly at a predetermined set-point temperature. The change in shape of the bi-metal disc is thus used to activate a mechanical switch. The bi-metallic disc element is mechanically interlocked with a pair of electrical contacts such that the rapid change in shape can be used to displace one or both of the electrical contacts to either make or break an electrical circuit. The electrical contacts may be provided as individual components mounted in a base structure, commonly known as a xe2x80x9cheader,xe2x80x9d or integrated into a conventional microswitch such that the necessity of assembling discrete components is substantially obviated. Examples of such of formations are described in U.S. Pat. Nos. 3,748,888 and 3,933,022, each of which is incorporated herein by reference in its entirety, wherein a thermally responsive, snap-action bi-metallic disc is provided.
FIG. 1 is a cross-sectional view that illustrates one known modular bi-metallic thermal switch device 10 having a bi-metallic disc actuator 12 positioned to drive relatively movable electrical contacts 14 and 16. The bi-metallic disc actuator 12 is embodied as a thermally responsive, snap-action bimetallic disc actuator that provides a snap force F generated during transit between bi-stable states at a predetermined set-point temperature. The electrical contacts 14, 16 are mounted on the ends of a pair of spaced-apart, electrically conductive terminal posts 20, 22 that are mounted in a header 24 such that they are electrically isolated from one anther. For example, terminal posts 20, 22 are mounted in the metallic header 24 using a glass or epoxy electrical isolator (not shown).
As illustrated in FIG. 1, the movable contact 16 is affixed to an electrically conductive carrier 28 that is embodied as an armature formed of an electrically conductive spring material. The armature 28 is affixed in turn in a cantilever fashion to the electrically conductive terminal post 22 such that a spring pressure S of the armature 28 operates to bias the movable contact 16 toward the fixed contact 14 to make electrical contact therewith. The electrical contacts 14, 16 thus provide an electrically conductive path between the terminal posts 20, 22 such that the terminal posts 20, 22 are shorted together.
The disc actuator 12 is spaced away from the header 24 by a spacer ring 30 interfitted with a peripheral groove 32. A substantially cylindrical case 34 fits over the spacer ring 30, thereby enclosing the terminal posts 20, 22, the electrical contacts 14, 16, and the disc actuator 12. The case 34 includes a base 36 with a pair of annular steps or lands 38 and 40 around the interior thereof and spaced above the base 36. The lower edge of the spacer ring 30 abuts the upper case land 40. A peripheral edge portion 42 of the disc actuator 12 is captured within an annular groove created between the lower end of the spacer ring 30 and the lower case land 38. The disc actuator 12 operates the armature spring 28 to separate the contacts 14, 16 through the distal end 44 of an intermediary striker pin 46 fixed to the armature spring 28. Separation of the contacts 14 and 16 creates an open circuit condition.
FIG. 2 is a cross-sectional view that illustrates another known modular bi-metallic thermal switch device 50 having the bi-metallic disc actuator 12 positioned to drive relatively movable electrical contacts (not shown) within a conventional microswitch 52. The closing and opening of the contacts respectively shorts together terminal posts 54, 56 to create a closed circuit condition or separates the contacts to create an open circuit condition. The disc actuator 12 is mounted on the annular step or land 38 around the interior thereof and spaced above the base 36 of the cylindrical case 34. According to one embodiment, a lower edge of a spacer ring 58 abuts the upper case land 40 and captures the peripheral edge portion 42 of the disc actuator 12 within an annular groove created between the lower end of the spacer ring 58 and the lower case land 38. The spacer ring 58 spaces the microswitch 52 away from the disc actuator 12 to an extent that the disc actuator 12 is positioned in operational relationship with the electrical contacts through the distal end 60 of an intermediary striker pin 62 projecting from the casing of the microswitch 52. An adhesive joint 64 fixes the microswitch 52 within the case 34 and secures the operational relationship with the disc actuator 12.
Often, the thermal switch devices 10, 50 are constructed and stocked in inventory as modular units, as shown in FIGS. 1 and 2, and mated with a mounting adapter 66 configured to match a particular application. For example, mounting adapters 66 are provided as flanged (shown), studded, or tubular adapters. Such mounting hardware is typically manufactured and stocked as separate components to maximize flexibility with minimum inventory. When a thermal switch having a specific response temperature is desired, the appropriate thermal switch module 10, 50 is selected from the inventory of modular units, and the mounting adapter 66 is selected to adapt the thermal switch module 10, 50 to the particular application.
In general, the thermal switch module 10, 50 is mated with the flanged, studded or other mounting adapter 66 at the time the device is ordered. Presently, the mounting adapter 66 is attached to the switch module 10, 50 by adhesive bonding (shown, using a known potting compound to form an adhesive joint 68) or other time-intensive methods, such as spot welding. The mating process thus delays order shipment and adds additional cost to the finished thermal switch product.
The present invention provides a method and apparatus for quick mating of modular thermal switch devices with different mounting hardware by providing a snap action interlocking mechanism, in contrast to the prior art devices and methods.
The apparatus and method of the present invention is a thermal switch apparatus having an adapter mount that snaps to a modular thermal switch by hand or with the use of a simple tool. The invention facilitates rapid, low cost assembly and shipment of thermal switch devices adapted to a predetermined external apparatus.
According to one aspect of the invention, the apparatus of the invention is embodied as a thermal switch apparatus including an adapter having a mounting apparatus and a receptacle, the receptacle having a female portion structured internally with a retainer; and a modular thermal sensing device having a male portion sized to enter the female portion of the receptacle, the male portion having an external relief structured to interlock with the internal retainer of the female portion.
According to another aspect of the invention, the male portion of the thermal sensing device is installed in the female portion of the adapter with the external relief being interlocked with the retainer.
According to another aspect of the invention, the external relief of the thermal sensing device is embodied as one or more recesses receded into an external surface of the male portion; and the retainer of the adapter is embodied as one or more projections extending inwardly of an interior wall portion of the receptacle, the projections cooperating with the recesses to secure the male portion of the thermal sensing device within the female portion of the receptacle.
According to another aspect of the invention, the retainer is embodied as an integral portion of the female portion of the receptacle.